TAMPA, Fla. (AP) — Mitt Romney is stepping up for the most important speech of his Republican presidential campaign, to an audience of millions, after a rousing warm-up from a running mate who vowed the days of dodging painful budget choices will end if voters toss President Barack Obama from office.

Having grasped the nomination on his second try, after years spent cultivating this moment, Romney will use his speech Thursday night to introduce himself to a large portion of voters and claw for advantage in a race that could scarcely be any closer. As part of that introduction, Romney appeared prepared to discuss his Mormon faith in more direct terms than usual, a direction signaled by running mate Paul Ryan on Wednesday night in several allusions to the duo's differing religions but "same moral creed."

The Wisconsin congressman, a deficit hawk who's become the party's darling since joining the ticket, offered a prime-time testimonial setting up Romney's turn on the stage in the Republican National Convention's finale. If history is a guide, viewership of Romney's speech — and Obama's address to his Democratic convention next week — will be surpassed only by the audience for their coming debates.

The Republican convention's most rah-rah moments were unfolding as Hurricane Isaac, down to a tropical storm, inflicted floodwaters and misery in rural stretches of nearby Gulf states. The slowly unfolding calamity went unmentioned by most key speakers Wednesday night, although a few asked for Red Cross donations to the victims and offered prayers. The GOP had cut the convention's opening day in fear Isaac would strike Tampa, which was spared.

Not that Obama set politicking aside, either, even as he tended to emergency management. Locked in an unpredictable race that shows no clear advantage for either man, Obama implored young people in a crowd of 7,500 in Charlottesville, Va., home to the University of Virginia, to register, vote and make sure their friends do as well. "I need you," he said. "America needs you to close the gap between what is and what might be."

Ryan, 42, came on board the campaign for the White House with a reputation in Washington for taking on the sacred cows in government spending, Medicare prime among them, and he's generated plenty of excitement among conservatives who have never been fully convinced that Romney is one of them. "I think he's a rock star for the Republicans," Allie Burgin, a delegate from Wynnewood, Okla., said before the speech. And that's how he was received on the stage.

"The present administration has made its choices," Ryan said, "and Mitt Romney and I have made ours. Before the math and the momentum overwhelm us all, we are going to solve this nation's economic problems. And I'm going to level with you: We don't have much time."

He was particularly cutting in his indictment of the president, even in a convention loaded with anti-Obama rhetoric. "Fear and division are all they've got left," he said. "It all started off with stirring speeches, Greek columns, the thrill of something new. Now all that's left is a presidency adrift, surviving on slogans that already seem tired, grasping at a moment that has already passed."

Ryan misrepresented Obama's record at times — and seemed to forget his own.

He said sharply that "the biggest, coldest power play of all in Obamacare came at the expense of the elderly. ... So they just took it all away from Medicare. Seven hundred and sixteen billion dollars, funneled out of Medicare by President Obama."

In fact, Ryan himself incorporated the same cuts into budgets he steered through the House in the past two years as chairman of its Budget Committee, using the money for deficit reduction. The cuts do not affect Medicare recipients directly, but rather reduce payments to hospitals, health insurance plans and other service providers.

Moreover, Ryan's own plan to remake Medicare would squeeze the program's spending even more than the changes Obama made.

Ryan promised, "We will not duck the tough issues; we will lead." But Romney has yet to flesh out those fiscal choices.

He's promised big increases in military spending and the restoration of more than $700 billion in Medicare cuts, along with lower taxes, without detailing how he would make good on his pledge to cut $500 billion a year from the federal budget. That goal is only realistic if budget cutters dive into the massive entitlements of Social Security and Medicare and if Congress can be persuaded to slice deeply into areas of spending such as health research, transportation, homeland security and aid to the poor.

In remarks to the American Legion in Indianapolis, Romney reaffirmed his intention to expand the armed forces and roll back "reckless defense cuts" that will begin automatically in January if Congress does not act to stop them. "There are plenty of places to cut in a federal budget that now totals over $3 trillion, but defense is not one of them," he said. Left unstated was that his running mate voted to approve the legislation that authorized those cuts alongside reductions in domestic spending.

Romney spokesman Kevin Madden said days earlier that the nominee would discuss his Mormon religion in his convention address as part of "what's informed his values." Ryan, a Roman Catholic, took up the matter conspicuously, and no doubt as part of the convention's carefully crafted message.

"Mitt and I also go to different churches," he said. "But in any church, the best kind of preaching is done by example. And I've been watching that example. The man who will accept your nomination tomorrow is prayerful and faithful and honorable. Not only a defender of marriage, he offers an example of marriage at its best. Not only a fine businessman, he's a fine man, worthy of leading this optimistic and good-hearted country."

And again: "Our different faiths come together in the same moral creed. We believe that in every life there is goodness; for every person, there is hope. Each one of us was made for a reason, bearing the image and likeness of the Lord of Life."

Former pastor Mike Huckabee, in his speech earlier, also delved into the subject, saying, "I care far less as to where Mitt Romney takes his family to church than I do about where he takes this country."

Arizona Sen. John McCain, the man who defeated Romney for the 2008 nomination only to lose the election to Obama, spoke on his 76th birthday and said he wished he'd been there under different circumstances. And an array of ambitious younger elected officials, Sens. Rand Paul of Kentucky and John Thune of South Dakota among them, preceded Ryan to the podium.

Former Secretary of State Condoleezza Rice praised the Republican ticket in a speech that made no overt mention of Obama. "Mitt Romney and Paul Ryan will rebuild us at home and inspire us to lead abroad. They will provide an answer to the question, 'Where does America stand?'"